1. Field of the Invention
This invention relates to a pressure force adjusting mechanism in an annular vibration wave driven motor for causing an elastic member in which a travelling vibration wave is formed and a movable member to be pressed with a predetermined pressure force.
2. Related Background Art
A vibration wave driven motor is generally such that a movable member is urged against a metallic elastic member formed, for example, into an annular shape and in which a travelling vibration wave is formed and the movable member is frictionally driven by a travelling vibration wave excited in the elastic member and the pressure force of the elastic member and the movable member affects the performance of the motor. Therefore, provision is made of a pressure force adjusting mechanism for applying a set pressure force.
Heretofore, a pressure force adjusting mechanism for a vibration wave driven motor has usually used n adjusting washer between a pressing member (a conical disk-spring) and a fixed member to make the amount of flexure of the pressing member constant to thereby adjust it to a set pressure force value. Also, another pressure force adjusting mechanism has made the amount of flexure of the pressing member constant by the manner in which a nut or the like is fastened, to thereby adjust it to a set pressure force value.
However, in the case of prior-art pressure force adjusting mechanisms which use an adjusting washer, it is very cumbersome to incorporate the adjusting washer, and adjustment is such that the amount of flexure of the pressing member is made constant, whereby it is adjusted to the set pressure force value. However, because of the pressure irregularity in the spring characteristic value of individual pressing members, it is difficult to adjust the amount of flexure to a set pressure force value only by setting the amount of flexure. To solve this problem, the spring characteristics of individual pressing members may be measured in advance, the amount of flexure may be determined in view of the characteristic values thereof, and the force may be adjusted by the use of an adjusting washer. However, in this case mass production is difficult and it very cumbersome to adjust or to measure the spring characteristics of individual pressing members. This has led to the disadvantage that considerable time is spent for the adjustment.
The latter system in which a nut or the like is fastened is a method of making the amount of flexure of the pressing member constant by the manner in which the nut or the like is fastened. However, in this case, the amount of flexure is used for pressing, and the aforementioned problem arises. To solve this problem, it would also occur to convert the pressure force of the pressing member into nut fastening torque and adjust it to a set pressure force value. However, but in such method, it is necessary to effect adjustment with friction torque which is produced when the nut is rotated. This has led to the disadvantage that an error due to the irregularity of the friction torque is added and it becomes considerably difficult to adjust the pressure force to a set pressure force value.